Gem‐disubstituted 4‐oxocyclohexanes: Source for spiro heterocycles

Novel spiro heterocycles, substituted spiro‐pyrimidine, pyrazole and isoxazole compounds are prepared by the cyclocondensation of 4‐oxocyclohexane gem‐dicarboxylates and cyano esters with nucleophiles.     

1,N-Etheno-2′-deoxytubercidin and pyrrolo-C: synthesis, base pairing, and fluorescence properties of 7-deazapurine nucleosides and oligonucleotides

The synthesis of 1,N⁶-etheno-7-deaza-2′-deoxyadenosine (12b) which was prepared from 7-deaza-2′-deoxyadenosine (5a) with chloroacetaldehyde is described. Also the regioselective glycosylation of the 7-deazapurine-2-one at nitrogen-1 (19) furnishing the pyrrolo-C nucleoside 7a is reported and a side chain derivative with a terminal triple bond (7d) is prepared. The fluorescence properties of these nucleosides and related compounds were determined. The etheno nucleoside 12b is strongly fluorescent showing a Stokes shift of 134 nm and a quantum yield of Φ=0.53. It proved to be stable, both in acidic and in alkaline medium while the parent purine compound 10b is labile under both conditions. Compound 12b was converted into its phosphoramidite 14 and was incorporated into oligonucleotides. Compound 12b destabilizes oligonucleotide duplexes when it is located in the center of the molecule; it stabilizes when it is incorporated in the terminal base pair or acts as an overhanging nucleoside. Temperature-dependent fluorescent measurements yielded sigmoidal melting profiles when compound 12b is stacked to the terminal base pair while a linear decrease of the fluorescence is observed when the molecule is located opposite to the four canonical nucleosides in the center of the duplex.     

Thermal analysis of a flow of immiscible couple stress fluids in a channel

An analytical study of the entropy generation rate and heat transfer in a flow of immiscible couple stress fluids between two horizontal parallel plates under a constant pressure gradient is performed. Both plates are kept at different and constant temperatures higher than that of the fluid. The Stokes couple stress flow model is employed. The classical no-slip condition is prescribed at the plates, and continuity of the velocity, rotation, couple stress, shear stress, temperature, and heat flux is imposed at the interfaces. The velocity and temperature distributions are found analytically, and they are used to compute the entropy generation number and Bejan number. The effects of the couple stress parameter and Reynolds number on the velocity, temperature, entropy generation number, and Bejan number are investigated. It is observed that the friction near the plates in couple stress fluids decreases as the couple stress increases.     

Cycloaddition of bis‐1,3‐dipolar reagents to 1,3‐diarylprop‐2‐en‐1‐ones

Bis pyrazolines and isoxazolines were prepared by 1,3‐dipolar cycloaddition of benzene‐1,3/1,4‐dicarboxaldehyde dihydrazones and dioximes to 1,3‐diaryl‐prop‐2‐en‐1‐ones. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:379–383, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10169     

The effect of silica substitution on electrical conduction in nickel ferrite

The electrical conductivity and Seebeck coefficient for nickel ferrite and nickel ferrite with 5% silica has been studied as a function of temperature. The lattice constant and the existence of a single phase are established from X-ray studies. Both the ferrites exhibit a transition near the Curie temperature with a change in slope of the conductivity (log σT) versus temperature (10³/T) curves. It is found that the activation energy in the paramagnetic region is higher than that in the ferrimagnetic region for both the ferrites.     

Halogen-substituted amides. VII—normal coordinate analysis of 2-fluoroacetamide and 2-iodoacetamide

A 30-parameter modified valence force field has been employed for a normal coordinate analysis of the in-plane vibrations of 2-fluoroacetamide and 2-iodoacetamide. The force constants have been refined using an overlay leastsquares technique. The potential energy distributions and eigen vectors have been used to make unambiguous vibrational assignments.